Average and Local Structural Origins of the Optical Properties of the Nitride Phosphor La3–xCexSi6N11 (0 < x ≤ 3)

Negative Thermal Quenching of Photoluminescence: An Evaluation from the Macroscopic Viewpoint

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors are reported to have exhibited NTQ. In this paper, a collection of results in the archival literature about NTQ of specific phosphors is discussed from a macroscopic viewpoint, focusing on the following three aspects: (1) Could the NTQ of a given phosphor be reproducible? (2) Could the associated data for a given phosphor exhibiting NTQ be in line with the law of the conservation of energy? (3) Could the NTQ of a given phosphor be demonstrated in a prototype WLED device? By analyzing typical cases based on common sense, we hope to increase awareness of the issues with papers reporting the NTQ of specific phosphors based on spectral intensity, along with the importance of maintaining stable and consistent measurement conditions in temperature-dependent spectral intensity measurement, which is a prerequisite for the validity of the measurement results.

Recent Developments of Microscopic Study for Lanthanide and Manganese Doped Luminescent Materials

Luminescent materials are indispensable for applications in lighting, displays and photovoltaics, which can transfer, absorb, store and utilize light energy. Their performance is closely related with their size and morphologies, exact atomic arrangement, and local configuration about photofunctional centers. Advanced electron microscopy-based techniques have enabled the possibility to study nanostructures with atomic resolution. Especially, with the advanced micro-electro-mechanical systems, it is able to characterize the luminescent materials at the atomic scale under various environments, providing a deep understanding of the luminescent mechanism. Accordingly, this review summarizes the recent achievements of microscopic study to directly image the microstructure and local environment of activators in lanthanide and manganese (Ln/Mn²⁺ )-doped luminescent materials, including: 1) bulk materials, the typical systems are nitride/oxynitride phosphors; and 2) nanomaterials, such as nanocrystals (hexagonal-phase NaLnF₄ and perovskite) and 2D nanosheets (Ca₂ Ta₃ O₁₀ and MoS₂ ). Finally, the challenges and limitations are highlighted, and some possible solutions to facilitate the developments of advanced luminescent materials are provided.

Post-doping induced morphology evolution boosts Mn2+ luminescence in the Cs2NaBiCl6:Mn2+ phosphor

As we know, defects caused in the synthetic process of metal halide perovskite are the most difficult to overcome, and greatly limit their photoelectric performances. Herein, a post-doped strategy was utilized to achieve an interesting morphology evolution from a standard octahedron to a snowflake-like sheet during the Mn²⁺-doped Cs₂NaBiCl₆ process, which realizes the obvious photoluminescence quantum efficiency (PLQY) enhancement of the Cs₂NaBiCl₆:Mn²⁺ phosphor. This surprising evolution is ascribed to the morphology collapse and reconstruction induced by Mn²⁺ exchange. The obtained phosphor exhibits enhanced 31.56% PLQY, which is two-fold higher than that synthesized by the traditional co-precipitation method, with broad emission spectrum and good PL color stability at 150 °C. Combined with the Cs₂SnCl₆ : 1mol%Bi³⁺ phosphor to fabricate the phosphor-converted light-emitting diode, bright white light emission with Ra = 88, CCT = 4320 K, CIE (0.36, 0.33) and a good application potential in high-resolution PL imaging agents was obtained. This work provides a possible effective strategy to improve the PL performance for impurity-doped lead-free metal halide perovskite.

Enhancement in the water resistance and thermal stability of Na3HTiF8:Mn4+ by co-doping with organic amine cations

Organic amine ions change the structural rigidity and improve the thermal stability and water resistance of phosphors.

Improvement of thermal stability and photoluminescence in Mg2Y2Al2Si2O12:Ce3+ by the cation substitution of Ca2+, Sr2+ and Ba2+ ions

The luminescence of Ce³⁺ in Mg₂Y₂Al₂Si₂O₁₂ (MgYAlSiO₆) can be controlled by substituting with Ca²⁺, Sr²⁺, and Ba²⁺ ions. The materials show blue shifts in their emission spectra that become highly evident with the increase in the ionic radius, and this phenomenon is the result of the combined action of the nephelauxetic effect and crystal field splitting. Due to the introduction of Ca²⁺, Sr²⁺, and Ba²⁺, the distortion of the crystal decreases and the structural rigidity and stability increase, improving the quantum efficiency and temperature stability of Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺. Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,Ca²⁺ is more stable than Mg₂Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,Sr²⁺/Ba²⁺ because the radius of Sr²⁺/Ba²⁺ is larger than that of Mg²⁺. The Mg_1.9Y_1.93Al₂Si₂O₁₂:0.07Ce³⁺,0.1Ca²⁺ fluorescent powder and blue chip were packaged to obtain warm white light-emitting diodes (LEDs) with luminous efficiency of 60 lm W^-1. These results show that the Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺ phosphor has potential application value in white LEDs.

Luminescence and Energy Transfer of Color-Tunable Y2Mg2Al2Si2O12:Eu2+,Ce3+ Phosphors

Color-tunable phosphors can be obtained through codoping strategies and energy transfer regulation. Ce³⁺ and Eu²⁺ are the most common and effective activator ions used in phosphor materials. However, the energy transfer from Eu²⁺ to Ce³⁺ is rarely reported. In this work, Y₂Mg₂Al₂Si₂O₁₂(YMAS):Eu²⁺,Ce³⁺ phosphors were successfully synthesized, which was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Rietveld refinement, scanning electron microscopy (SEM) and element mapping images, and spectral information. The luminescent color of YMAS:Eu²⁺,Ce³⁺ phosphors could be tuned from blue to cyan to light green to yellow-green and finally to green-yellow, which was achieved by adjusting the energy transfer between different dopants. The energy transfer from Eu²⁺ to Ce³⁺ was confirmed by photoluminescence spectra and fluorescence decay curves. Within the experimental gradient, the energy transfer efficiency could reach up to 48%. At 373 K, the Y_1.99Mg_1.99Al₂Si₂O₁₂:0.01Eu²⁺,0.01Ce³⁺ (YMAS:0.01Eu²⁺,0.01Ce³⁺) phosphor exhibited a total integral emission loss of only 8%, and the emission peak intensity decreased to 95%, indicating the excellent thermal stability. The white light-emitting diode (WLED) fabricated by the YMAS:0.01Eu²⁺,0.01Ce³⁺ phosphor has the same level correlated color temperature (CCT = 5841 K), greatly improved color rendering index (R_a = 87.8), and higher quality white light color (CIE = (0.3258, 0.3214)) than the WLED made by the YMAS:0.01Eu²⁺ phosphor, indicating that the performance of the phosphor was significantly improved by introducing Ce³⁺. This work provides an effective guide for the design and development of highly efficient color-tunable phosphors involving energy transfer from Eu²⁺ to Ce³⁺ in some specific materials, such as garnet structures.

Achievement of narrow-band blue-emitting phosphors KScSr1-y Ca y Si2O7:Bi3+ by the migration of luminescence centers

In recent years, efforts have been made to develop narrow-band emission phosphors with excellent performance. Herein, a series of KScSr1-y Ca y Si2O7:0.07Bi3+ narrow-band phosphors were synthesized by a co-substitution method, and the crystal structure, the occupancy of activated ions and luminescence properties were studied in detail. The substitution of Ca2+ for Sr2+ ions resulted in the migration of the activated Bi3+ from the K site to Sr site, accompanied by the regulation of the emission peak from 410 nm to 455 nm, the peak emission half width from 52 nm to 40 nm, and the color purity from the original 78% to 88%. In addition, a warm white LED with low CCT = 3401 K, CRI = 95.5, and CIE color coordinates of (0.3447, 0.3682) has been obtained through the combination of KSS0.6C0.4S:0.07Bi3+ with a commercial green and red phosphor on a UV (370 nm) chip. The results not only provided a strategy based on the manipulation of chemical composition and crystal structure to tune spectral distribution, but also broadens the choice of activators of narrow-band blue-emitting phosphors.

Achieving the potential multifunctional near-infrared materials Ca3In2-x Ga x Ge3O12:Cr3+ using a solid state method

Near-infrared spectroscopy is developing rapidly in the fields of human detection and food analysis due to its fast response and non-invasive characteristics. Herein, we report the novel near-infrared garnet-type Ca3In2Ge3O12:xCr3+ and Ca3In2-x Ga x Ge3O12:0.07Cr3+ phosphors, in which there are two crystallographic sites (CaO8, InO6) that can be substituted by Cr3+, and cation regulation engineering for In3+ is utilized to tune the luminescence properties. Under the 480 nm excitation, the Ca3In2Ge3O12:xCr3+ phosphor emits a broad spectrum at 650-1150 nm, which matches well with the first biological window. The concentration quenching mechanism and luminescence mechanism of Ca3In2Ge3O12:xCr3+ were studied and the site assignment of the two luminescence centers was discussed using low temperature spectra and fluorescence decay curves. The application performance of the phosphor was improved by introducing Ga3+ to substitute for In3+, and the blue shift of nearly 50 nm was explained by crystal field and nephelauxetic effects. At the same time, a 24% increase in the activation energy of thermal quenching of phosphors was obtained, which has been analyzed using the mechanism of phonon transition and the change of structural rigidity. Thus, the near-infrared emitting Ca3In0.2Ga1.8Ge3O12:0.07Cr3+ phosphor was obtained, which has lower cost, higher emission intensity, and much better thermal stability, spreading the application of phosphors in plant far red light illumination, human body detection, and spectral conversion technology of silicon-based solar cells. Simultaneously, an example of a near-infrared plant illumination experiment is given, demonstrating that a cation substitution strategy based on crystal field control could be applied to tune spectral distribution and develop novel potential phosphors for practical optical application.

Enhancing Structural Rigidity via a Strategy Involving Protons for Creating Water-Resistant Mn4+-Doped Fluoride Phosphors

The poor water resistance property of a commercial Mn⁴⁺-activated narrow-band red-emitting fluoride phosphor restricts its promising applications in high-performance white LEDs and wide-gamut displays. Herein, we develop a structural rigidity-enhancing strategy using a novel KHF₂:Mn⁴⁺ precursor as a Mn source to construct a proton-containing water-resistant phosphor K₂(H)TiF₆:Mn⁴⁺ (KHTFM). The parasitic [HMnF₆]^- complexes in the interstitial site from the fall off the KHF₂:Mn⁴⁺ are also transferred to the K₂TiF₆ host by ion exchange to form KHTFM with rigid bonding networks, improving the water resistance and thermostability of the sample. The KHTFM sample retains at least 92% of the original emission value after 180 min of water immersion, while the non-water-resistant K₂TiF₆:Mn⁴⁺(KTFM) phosphor maintains only 23%. Therefore, these findings not only illustrate the effect of protons on fluoride but also provide a novel insight into commercial water-resistant fluoride phosphors.

Understanding the abnormal lack of spectral shift with cation substitution in highly efficient phosphor La3Si6N11:Ce3

Cation substitution is a common strategy to tune the luminescence by modulating the cell parameter, polyhedral volume and bond length in solid-solution-type phosphors. Generally a close correlation between their cationic composition and spectral peak shifts can be observed. In certain compounds, however, luminescence tuning by cationic modification is almost invalid. This work is devoted to providing a reasonable explanation for the anomaly in Ce³⁺ doped La₃Si₆N₁₁, which demonstrates unshifted excitation peaks with various cation substitutions. By simplifying the local coordination polyhedron that accommodates Ce³⁺ to a truncated square pyramid model, the quantitative crystal-field calculations are conducted to demonstrate the influences of the coordination environment on energy levels. The results show that the crystal-field levels become insensitive to this special type of ligand environment, leading to imperceptible peak shifts. Therefore, the relationship between the cationic composition and luminescence is determined not only by the ionic radii but also by the type of coordination polyhedron. This work shows that studying the coordination environment is helpful for achieving effective luminescence tuning.

Highly Luminous N3--Substituted Li2MSiO4-δN2/3δ:Eu2+ (M = Ca, Sr, and Ba) for White NUV Light-Emitting Diodes

The N^3--substituted Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors were systematically prepared and analyzed. Secondary-ion mass spectroscopy measurements revealed that the average N^3- contents are 0.003 for Ca, 0.009 for Sr, and 0.032 for Ba. Furthermore, the N^3- incorporation in the host lattices was corroborated by infrared and X-ray photoelectron spectroscopies. From the photoluminescence spectra of Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors before and after N^3- doping, it was verified that the enhanced emission intensity of the phosphors is most likely due to the N^3- doping. In Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors, the maximum wavelengths of the emission band were red-shifted in the order Ca < Ba < Sr, which is not consistent with the trend of crystal field splitting: Ba < Sr < Ca. This discrepancy was clearly explained by electron-electron repulsions among polyhedra, LiO₄-MO _n , SiO₄-MO _n , and MO _n -M'O _n associated with structural difference in the host lattices. Therefore, the energy levels associated with the 4f⁶5d energy levels of Eu²⁺ are definitely established in the following order: Li₂CaSiO₄:Eu²⁺ > Li₂BaSiO₄:Eu²⁺ > Li₂SrSiO₄:Eu²⁺. Furthermore, using the Williamson-Hall (W-H) method, the determined structural strains of Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors revealed that the increased compressive strain after N^3- doping induces the enhanced emission intensity of these phosphors. White light-emitting diodes made by three N^3--doped phosphors and a 365 nm emitting InGaN chip showed the (0.333, 0.373) color coordinate and high color-rendering index (R _a = 83). These phosphor materials may provide a platform for development of new efficient phosphors in solid-state lighting field.

A Cerium Doped Scandate Broad Orange-Red Emission Phosphor and its Energy Transfer-Dependent Concentration and Thermal Quenching Character

A series of BaSr₂Sc₄O₉ and Ce³⁺-doped BaSr₂Sc₄O₉ phosphors were synthesized via the high temperature solid state reaction. Crystal structure information on BaSr₂Sc₄O₉ is first refined using the Rietveld method based on the XRD data, and it is assigned to the trigonal system with the R3 space-group. The photoluminescence properties were investigated in detail, including the emission and excitation spectra, site occupation, decay lifetime, thermal quenching, and quantum efficiency. There are three Ba²⁺/Sr²⁺ sites and four Sc³⁺ sites in this structure. The Ce³⁺ ions in the 6-fold coordinated Sr²⁺/Ba²⁺ sites show a near-ultraviolet-blue emission with a peak at around 407 nm under ultraviolet excitation. The Ce³⁺ ions in Sc³⁺ sites exhibit a bright broad orange-red emission with the peak at around 615 nm under near-ultraviolet and blue excitation. The energy transfer process between the different sites is demonstrated based on the spectral analysis, theoretical calculation, and decay lifetime variation. Under excitation of 345 nm, the energy transfer phenomenon and distribution of activator ions lead to the invalidation of part of the Ce³⁺ ions, and then it causes a higher concentration quenching point. The participation of the energy transfer in the thermal quenching phenomenon causes the abnormal intensity variation, which is ascribed to the energy compensation by the increasing energy transfer efficiency at high temperature. The internal quantum efficiency is 45% under the 420 nm excitation wavelength. An excellent white light emitting diode lamp is obtained by fabricating BaSr₂Sc₄O₉:Ce³⁺ with BAM:Eu²⁺, β-sialon:Eu²⁺, and a 395 nm GaN chip; its CIE coordinate ( x, y), CCT, and Ra are (0.3708, 3463), 4023 K, and 84. These results reveal the correlation between energy transfer and luminescent property and provide a practical foundation to comprehend and adjust the photoluminescence performance.

Identifying an efficient, thermally robust inorganic phosphor host via machine learning

Rare-earth substituted inorganic phosphors are critical for solid state lighting. New phosphors are traditionally identified through chemical intuition or trial and error synthesis, inhibiting the discovery of potential high-performance materials. Here, we merge a support vector machine regression model to predict a phosphor host crystal structure’s Debye temperature, which is a proxy for photoluminescent quantum yield, with high-throughput density functional theory calculations to evaluate the band gap. This platform allows the identification of phosphors that may have otherwise been overlooked. Among the compounds with the highest Debye temperature and largest band gap, NaBaB₉O₁₅ shows outstanding potential. Following its synthesis and structural characterization, the structural rigidity is confirmed to stem from a unique corner sharing [B₃O₇]^5– polyanionic backbone. Substituting this material with Eu²⁺ yields UV excitation bands and a narrow violet emission at 416 nm with a full-width at half-maximum of 34.5 nm. More importantly, NaBaB₉O₁₅:Eu²⁺ possesses a quantum yield of 95% and excellent thermal stability.

Identifying phosphors with good thermal stability and quantum efficiency is a prerequisite to improve the performance of white LED light sources. Here, a combined machine learning and density functional theory method is introduced to identify next generation inorganic phosphors.

Structure Transformation and Cerium-Substituted Optical Response across the Carbonitridosilicate Solid Solution (LaδY1-δ)2Si4N6C (δ = 0-0.5)

Following an investigation proving La₂Si₄N₆C crystallizes in a monoclinic space group, isostructural to Y₂Si₄N₆C, the reportedly hexagonal (La_0.5Y_0.5)₂Si₄N₆C was reinvestigated to examine the apparent crystal structure change across the solid solution. Initially, calculating the electronic structure and phonon density of states of (La_0.5Y_0.5)₂Si₄N₆C in the P6₃mc space group revealed an imaginary phonon mode, which is indicative of a structural instability. Displacing the atoms along the pathway of the imaginary vibration led to a previously unreported space group for carbonitridosilicates, trigonal P31c. The assignment of the trigonal space group was subsequently confirmed by synthesizing (La_0.5Y_0.5)₂Si₄N₆C using high-temperature, solid state synthesis and analyzing the crystal structure with high-resolution synchrotron X-ray powder diffraction. Preparing the solid solution, (La_δY_1-δ)_1.98Ce_0.02Si₄N₆C (δ = 0-0.5), showed that the crystal structure changes from the monoclinic to the trigonal space group at δ ≈ 0.25. Finally, substituting Ce³⁺ in the crystal structure to investigate the optical response via steady-state luminescent and photoluminescent quantum yield measurements reveals severe luminescent quenching with increasing La³⁺ content, due to a combination of absorption of luminescence by the host structure and thermal quenching. These results display the virtue of combining computational and experimental techniques to solve inorganic crystal structures and assess potential phosphor hosts.

Control of the photoluminescence in Ba0.97Y2Si3O10:Eu2+ phosphors via the intensification effect of the second luminescence centre

A method is reported that broadens the FWHMs of the emission spectra of Ba_0.97Y₂Si₃O₁₀:0.03Eu²⁺ by intensifying the second emission peak.

Discovery of novel solid solution Ca3Si3-x O3+x N4-2x : Eu2+ phosphors: structural evolution and photoluminescence tuning

Discovery of novel phosphors is one of the main issues for improving the color rendering index (CRI) and correlated color temperature (CCT) of white light-emitting diodes (w-LEDs). This study mainly presents a systematic research on the synthesis, crystal structure variation and photoluminescence tuning of novel (oxy)nitride solid solution Ca₃Si_3−xO_3+xN_4−2x: Eu²⁺ phosphors. XRD refinements show that lattice distortion occurs when x value diverges the optimum one (x = 1). The lattice distortion causes a widening of emission spectrum and an increase of Stokes shift (ΔSS), which leads to a bigger thermal quenching. With decrease of x value, the emission spectrum shows an obvious red-shift from 505.2 to 540.8 nm, which is attributed to the crystal field splitting. The enhanced crystal field splitting also broadens the excitation spectrum, making it possible to serve as the phosphor for near ultraviolet (n-UV) LEDs. A 3-phosphor-conversion w-LED lamp was fabricated with the as-prepared phosphor, which exhibits high CRI (Ra = 85.29) and suitable CCT (4903.35 K). All these results indicate that the Ca₃Si_3−xO_3+xN_4−2x: Eu²⁺ phosphor can serve as the green phosphor for n-UV w-LEDs, with a tunable spectrum by controlling the crystal structure and morphology.

Composition Screening in Blue-Emitting Li4Sr1+xCa0.97-x(SiO4)2:Ce3+ Phosphors for High Quantum Efficiency and Thermally Stable Photoluminescence

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Li₄Sr_1+xCa_0.97-x(SiO₄)₂:0.03Ce³⁺ (-0.7 ≤ x ≤ 1.0) phosphors were designed from the initial model of Li₄SrCa(SiO₄)₂:Ce³⁺, and their single-phased crystal structures were found to be located in the composition range of -0.4 ≤ x ≤ 0.7. Depending on the substitution of Sr²⁺ for Ca²⁺ ions, the absolute QE value of blue-emitting composition-optimized Li₄Sr_1.4Ca_0.57(SiO₄)₂:0.03Ce³⁺ reaches ∼94%, and the emission intensity at 200 °C remains 95% of that at room temperature. Rietveld refinements and Raman spectral analyses suggest the increase of crystal rigidity, increase of force constant in CeO₆, and decrease of vibrational frequency by increasing Sr²⁺ content, which are responsible for the enhanced quantum efficiency and thermal stability. The present study points to a new strategy for future development of the pc-LEDs phosphors based on local structures correlation via composition screening.

Energy transfer induced improvement of luminescent efficiency and thermal stability in phosphate phosphor

Ce3+ and Eu2+/Tb3+/Mn2+ ions codoped Ca6BaP4O17 (CBPO) phosphors have been prepared via a high-temperature solid state reaction. The structural refinement indicates that the as-prepared phosphors crystallize in monoclinic phase (C2/m) and there are two Ca sites and one Ba site in host lattice. The doping ions are determined to occupy Ca sites and the emission of Ce3+ and Eu2+ ions at different Ca sites were identified and discussed. Since bright blue and yellow emissions were observed from Ce3+and Eu2+ ions monodoped CBPO under n-UV excitation, respectively. They were codoped into the CBPO for designing energy transfer from Ce3+ to Eu2+ to improve the luminescence efficiency of Eu2+. In addition, Tb3+ ions were added into the CBPO:Ce3+ system for realizing highly efficient green emission. The energy transfer mechanisms from Ce3+ to Eu2+/Tb3+ ions were discussed. Interestingly, the incorporation of Mn2+ ions into the CBPO:Ce3+ system enhanced the blue emission of Ce3+ ions due to the modification of crystal lattice. Finally, the thermal stability of CBPO:Ce3+, Eu2+/Tb3+/Mn2+ phosphors were investigated systematically and corresponding mechanisms were proposed. Based on these results, the as-prepared CBPO:Ce3+, Eu2+/Tb3+/Mn2+ phosphors can act as potential blue, yellow, green, and emission-tunable phosphors for n-UV based white LEDs.

Recent developments in the new inorganic solid-state LED phosphors

The emerging new solid-state LED phosphors and the methodologies for their development have been reviewed in this perspective.

Structure and redshift of Ce3+ emission in anisotropically expanded garnet phosphor MgY2Al4SiO12:Ce3+

An overall compression with anisotropic expansion of the Ce³⁺ local environment resulted from incorporating Mg²⁺ into the Y³⁺ site. Insight into the crystal field splitting and the Stokes shift is given to interpret the Ce³⁺ emission redshift.

Effect of Y3+ on the local structure and luminescent properties of La3−xYxSi6N11:Ce3+ phosphors for high power LED lighting

A series of phase pure nitride yellow phosphors La_3−xY_xSi₆N₁₁:Ce³⁺ with good thermal stability and tunable luminescence properties have been synthesized and the crystal structure was investigated in detail.

Average and local structure, debye temperature, and structural rigidity in some oxide compounds related to phosphor hosts

The average and local structure of the oxides Ba2SiO4, BaAl2O4, SrAl2O4, and Y2SiO5 are examined to evaluate crystal rigidity in light of recent studies suggesting that highly connected and rigid structures yield the best phosphor hosts. Simultaneous momentum-space refinements of synchrotron X-ray and neutron scattering yield accurate average crystal structures, with reliable atomic displacement parameters. The Debye temperature ΘD, which has proven to be a useful proxy for structural rigidity, is extracted from the experimental atomic displacement parameters and compared with predictions from density functional theory calculations and experimental low-temperature heat capacity measurements. The role of static disorder on the measured displacement parameters, and the resulting Debye temperatures, are also analyzed using pair distribution function of total neutron scattering, as refined over varying distance ranges of the pair distribution function. The interplay between optimal bonding in the structure, structural rigidity, and correlated motion in these structures is examined, and the different contributions are delineated.

Recent progress in luminescence tuning of Ce3+and Eu2+-activated phosphors for pc-WLEDs

This review is devoted to several approaches to realize spectral tuning for improving the luminescence performance of Ce³⁺and Eu²⁺-activated pc-WLED phosphors.

La3Si6N11

Colorless transparent single crystals of trilanthanum hexa­silicon undeca­nitro­gen, La₃Si₆N₁₁, were prepared at 0.85 MPa of N₂ and 2273 K. The title compound is isotypic with Sm₃Si₆N₁₁. Silicon-centered nitro­gen tetra­hedra form a three-dimensional network structure by sharing their corners. Layers of one type of SiN₄ tetra­hedra and slabs composed of the two different La³⁺ cations and the other type of SiN₄ tetra­hedra are alternately stacked along the c axis of the tetra­gonal unit cell. The site symmetries of the two La³⁺ cations are are ..m and 4.., respectively.